The present invention relates to implantable medical leads, and more particularly implantable pacing/defibrillation leads for applications such as cardiac pacemaking or cardioversion, including heart stimulation and monitoring.
Implantable leads can be used to pass an electric current through the myocardium to alleviate arrhythmias, for example using the methods of cardioversion for tachycardia, defibrillation for ventricular fibrillation, and other methods depending on the particular arrhythmia. Alleviation of arrhythmias can be accomplished transvenously by implanting leads in the heart. The implantable leads form an electrical connection between a pulse generator or other electronic device and the heart.
Leads typically include one or more electrodes at the lead""s distal end. The electrodes are designed to form an electrical connection with a tissue or organ. A flexible conductor electrically connects the electrode to the pulse generator. Commonly, the flexible conductor takes the form of a single or multifilar wire coil. Although, stranded or solid cables are also used. Regardless of the form, an insulating layer of material typically surrounds the flexible conductors. Together, the flexible conductor and the insulating layer form the lead body. The lead body electrically and mechanically couples the pulse generator at its proximal end to the electrode at its distal end.
Transvenous cardioversion and defibrillation leads employ cardioversion and defibrillation electrodes, respectively. These electrodes are typically configured as elongated metal coils. Transvenous pacing leads, cardiac ablation catheters and other electrode bearing leads and catheters may also employ coil electrodes. Leads having coil electrodes are commonly manufactured by winding the wire into a helix around the exterior surface of the lead body. The winding of wire around the lead body typically creates a region of increased diameter relative to the lead body. The increased diameter is usually twice the wire""s diameter. Alternatively, a lead body may be attached to a separate coil electrode. A collar or transition is typically provided at the juncture of the lead body and a separate coil electrode. The collar or transition mechanically stabilizes the junction between the lead body and the separate coil electrode. The collar or transition also typically creates a region of increased diameter. The increased diameter resulting from the above methods is detrimental to the patient because they require an increased diameter introducer for implantation. The use of an increased diameter introducer increases the trauma to tissues during implantation. The increased diameter introducer also limits the size of the vein in which the electrode may be introduced. In addition, the collar or transition complicates the explanting of the lead by potentially xe2x80x9changing-upxe2x80x9d on a removal sheath used for this purpose and thereby, increases the risk to the patient. Alternatively, if no sheath is used, a danger of having the collar or transition xe2x80x9changing-upxe2x80x9d on fibrotic tissue exists during explanting. Thus, there is a need to provide a coil electrode having a uniform diameter junction with the lead body to produce an isodiametric lead.
The present invention meets the above needs and provides additional advantages and improvements that will be evident to those skilled in the art.
The present invention provides a lead that is substantially isodiametric over the region where the lead body transitions to coiled electrode. The present invention eliminates the need to use an increased diameter introducer to allow passage of a lead""s region of increased diameter and reduces or eliminates the possibility of a region of increased diameter creating a shoulder capable of xe2x80x9changing-upxe2x80x9d on the introducer, removal sheath or fibrotic tissue during implanting and explanting.
The lead includes a lead body and a coil electrode. The lead body includes at least one conductor and an elongated, flexible polymeric lead insulator surrounding the conductor. The lead body may also include additional pacing and/or sensing conductors. The individual conductors may be single wires or a plurality of wires. The lead insulator generally defines an outside diameter, an internal lumen and a counterbore at its distal end. The coil electrode includes a wire wound as a helix around an inner insulator. The inner insulator can define one or more additional lumens. The coil electrode has a coil diameter substantially equal in size to the outside diameter of the lead insulator. The coil electrode is electrically coupled to the conductor. The wire helix may be electrically coupled to the conductor by spirally winding the shocking coil around the shocking conductor, welding, crimping or a conductive adhesive. The inner insulator is secured within the counterbore of the lead insulator. The inner insulator may be frictionally secured, adhesively bonded or welded within the counterbore of the lead insulator. If the lead body has additional pacing or sensing conductors, a distal end of the pacing or sensing conductors extending distally beyond the counterbore in the distal end of the lead insulator and into the lumen of the inner insulator. Thereby, the lead insulator and the inner insulator continuously electrically insulate the pacing and/or sensing conductors from the coil electrode.
Alternatively, the inner insulator of the coil electrode defines the counterbore at its proximal end instead of the lead body defining a counterbore at its distal end. In this later embodiment, the lead insulator is secured within the counterbore of the inner insulator. Again, the lead insulator may be frictionally secured, adhesively bonded or welded within the counterbore of the inner insulator.